Organofunctional alkoxysilanes have established and broad utilities as coupling agents, adhesion promoters, or crosslinking agents in applications involving inorganic fillers and substrates, and organic polymers. Most of such organofunctional silanes in commercial use in terms of both volumes produced and breadth of applications have been trialkoxysilanes, i.e., having three reactive alkoxy groups attached to each silicon atom, in addition to one organofunctional group.
The chemistries leading to the related alkyldialkoxysilanes have also long been known, but these products have not achieved the same high level of commercial success and are not produced in similarly large commercial volumes. There are several reasons for these differences, and these differences are reflected in less efficient processes, lower yields, and higher prices for organofunctional alkyldialkoxysilanes, making them less accessible in the marketplace.
In Journal of the American Chemical Society, Vol. 81, pp. 2632-2635(1959), Plueddemann and Fanger report the respective reactions of dimethylethoxysilane, methyldiethoxysilane, and triethoxysilane with allyl glycidyl ether as giving single products in substantially quantitative yields without presenting purity data, while isomeric products were detected in a related hydrosilation of butadiene monoepoxide. In each case, the hydrosilyl reactant was added to the olefinic epoxide. In the same journal, Volume 79, pp. 3073-3077(1957), Goodman et al report the hydrosilations of vinyl ethyl ether, vinyl n-butyl ether, and allylidene diacetate with methyldiethoxysilane by adding the olefin to the silane.
When methyldiethoxysilane is treated with chloroplatinic acid under hydrosilation conditions, a hydrogen/alkoxy exchange reaction is reported, without alkyl/alkoxy exchange (Chemical Abstracts, Volume 82, abstr. 16884v(1975), in English as Journal of General Chemistry, USSR, Volume 44, pp. 1744-5(1974)). More recently, U.S. Patent No. 4,966,981 discloses hydrosilations of allyl glycidyl ether wherein added alcohol is used to attain high product purity by reducing the level of formation of internal adducts to the allyl group vs. the formation of desired terminal adducts. All examples are run by adding the SiH-containing reactant to a stoichiometric excess of the olefinic reactant.
The art discloses a methyl/trimethylsiloxy group exchange which occurs when internal olefins (2-hexene, cyclohexene) are hydrosilated with bis(trimethylsiloxy)methylsilane, (Me.sub.3 SiO).sub.2 MeSiH. Speier et al report in Journal of Organic Chemistry, Volume 30, pp. 1651-2 (1965) that such hydrosilations are accompanied by a methylltrimethylsiloxy group exchange.
While hydrosilation reactions have been run by adding the olefinic reactant to the hydrosilane on trialkoxy silanes, that mode has not been used generally because of safety hazards. See, for example, U.S. Pat. Nos. 4,160,775 and 5,559,264.
There appears to be no known example of alkyl/alkoxy group exchange reaction occurring during hydrosilation reactions of hydroalkyldialkoxysilanes with olefins. Alkyl/alkoxy group exchange reactions have been reported for simple methylalkoxysilanes at high temperatures with strong base catalysts, but these involve neither hydroalkyldialkoxysilanes nor hydrosilatable olefins. See Ryan, Journal of the American Chemical Society, Volume 84, p. 4730(1962).